linux-kernel - Re: [PATCH] sched/fair: Fix util_est UTIL_AVG

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Message-ID: <a8ab9455-a9be-2349-d23a-676aa89fbf2d@arm.com>
Date:   Fri, 28 May 2021 00:38:11 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Xuewen Yan <xuewen.yan94@...il.com>
Cc:     Vincent Donnefort <vincent.donnefort@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Quentin Perret <qperret@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: Fix util_est UTIL_AVG_UNCHANGED handling

On 27/05/2021 07:41, Xuewen Yan wrote:
> Hi
> 
> On Wed, May 26, 2021 at 10:59 PM Dietmar Eggemann
> <dietmar.eggemann@....com> wrote:
>>
>> On 19/05/2021 18:06, Vincent Donnefort wrote:
>>> On Fri, May 14, 2021 at 12:37:48PM +0200, Dietmar Eggemann wrote:

[...]

>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index c7e7d50e2fdc..0a0bca694536 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -357,6 +357,16 @@ struct util_est {
>>  #define UTIL_EST_WEIGHT_SHIFT          2
>>  } __attribute__((__aligned__(sizeof(u64))));
>>
>> +/*
>> + * This flag is used to synchronize util_est with util_avg updates.
>> + * When a task is dequeued, its util_est should not be updated if its util_avg
>> + * has not been updated in the meantime.
>> + * This information is mapped into the MSB bit of util_est.enqueued at dequeue
>> + * time. Since max value of util_est.enqueued for a task is 1024 (PELT util_avg
>> + * for a task) it is safe to use MSB.
>> + */
>> +#define UTIL_AVG_UNCHANGED 0x80000000
>> +
> 
> IMHO, Maybe it would be better to put it in the util_est structure
> just like UTIL_EST_WEIGHT_SHIFT?

Yeah, can do.

I just realized that 'kernel/sched/pelt.h' does not include
<linux/sched.h> directly (or indirectly via "sched.h". But I can easily
move cfs_se_util_change() (which uses UTIL_AVG_UNCHANGED) from pelt.h to
pelt.c, its only consumer anyway.